The present invention relates to a non aqueous, lithium battery cell and to a process for preparing such a battery cell. More particularly, the invention relates to such a battery cell employing the cell components in a substantially constant volume and employing a cathode active material which upon discharge intercalates and undergoes a phase transition to a distinct structural phase, which phase produces a cathode expansion.
U.S. Pat. No. 4,224,390 discloses a non-aqueous, lithium battery cell including as the cathode active material MoS.sub.2. In particular, this patent discloses that a secondary lithium battery having good reversible characteristics can be provided by discharging a non-aqueous, lithium/MoS.sub.2 battery cell under certain conditions so that certain phase transitions occur within the lithium intercalated MoS.sub.2. The patent discloses advantageous phases referred to as "Phase 2" and "Phase 3" and discloses that, when the cathodes of such batteries are operated with the cathodes maintained within these phases, the cathodes provide good reversibility.
Co-pending U.S. application Ser. No. 403,286, filed July 29, 1982, broadly discloses and claims the principle that, by applying a compressive load to a lithium electrode especially during recharging thereof in a non-aqueous battery cell system, it is possible to inhibit the formation of a porous deposit of exterior, irregularly oriented, amalgamated lithium grains on the anode, which grains have been recognized in the art as decreasing the reversibility of the lithium anodes. The compressive load provides a substantially non-porous lithium deposit on the anode, which allows enhanced reversibility for the lithium anode. The prior patent application also discloses the use of MoS.sub.2 as a cathode active material in connection with that invention. While this prior application broadly discloses and claims the principle of using a compressive load on the lithium electrode to provide the desired inhibition, the specific embodiments disclosed therein employ mechanical elements separate from the cell components themselves for providing the compressive load, e.g., a spring, C-clamp. etc.
Moreover, X-ray data had been developed during the course of the work in connection with the invention disclosed in U.S. Pat. No. 4,224,390 that indicated that the unit cell volume of the Li.sub.x MoS.sub.2 in "Phase 2" as described in U.S. Pat. No. 4,224,390 increased in volume, but less than the decrease in volume of lithium during discharge, i.e., the net change in the volume of the cell from such information would be expected to decrease. Thus, it could not have been expected that cathode expansion with an MoS.sub.2 cathode active material could be employed to create a compressive load on the lithium anode, let alone a sufficient compressive load to provide the results as disclosed in application Ser. No. 403,286.
Certain other cathode materials are known to expand upon cell discharge in non-aqueous, lithium batteries. For example, Kaduboski U.S. Pat. No. 4,129,686 discloses that solid cathodes such as FeS.sub.2 expand upon discharge. The Kaduboski patent, however, employs such cathode expansion in a lithium primary cell as shown in FIGS. 1 and 2 of the patent in combination with a conductive member 20 having protusions 26 embedded in the anode which will provide a shorting out of the cell when the anode is discharged to a predetermined extent, i.e., the protrusions break through the separator and contact the expanding cathode to short the cell. This is said to avoid distortion of the overall dimensions of the cell. In fact, the Kaduboski patent suggests that in instances where the negative electrode maintains its contour during discharge or for cells that may bulge prematurely, only a portion of the protusions be embedded in the anode (i.e., that a gap be left) so that upon expansion of the cathode, the anode will be forced back against the base of the conductive member.